The present invention relates to pumps, and more particularly, to diaphragm pumps having a relatively small displacement.
Diaphragm pumps are commonly used to pump gases or liquids in fluid systems which do not require a high volume flow rate of fluid. A diaphragm pump typically includes a housing forming a pump chamber, a flexible diaphragm attached to the housing and located within the chamber, a motor having an eccentrically rotating drive shaft, a connecting rod attached at one end to the diaphragm and at an opposite end to the drive shaft, and inlet and outlet valves communicating with the pump chamber and having fittings for connecting the pump to the remainder of the fluid system. The rotational motion of the eccentric drive shaft of the motor is transmitted by the connecting rod to the diaphragm, and causes the diaphragm to be flexed within the chamber, thereby alternately increasing and decreasing the effective volume of the chamber. This change of volume alternately draws fluid into the chamber through the inlet valve and forces fluid from the chamber through the outlet valve.
A typical example of such a diaphragm pump is shown in Hagen et al. U.S. Pat. No. 4,086,036. In that pump, the eccentric drive shaft is press fitted within the inner race of a ball bearing bushing. The connecting rod is attached to a clamp which is fitted about the outer race of the ball bearing bushing. The connecting rod is supported within the pump by the diaphragm at an upper end and by the bearing races at a lower end, so that movement of the connecting rod and diaphragm is constrained by the engagement between the inner bearing race and the eccentric drive shaft of the motor.
Since the diaphragm is annular in shape, reactive forces are exerted against the connecting rod during operation in all directions, which are transmitted back to the eccentric drive shaft. Therefore, forces are exerted on the drive shaft and its mounting bearings within the motor which are parallel to the rotational axis, perpendicular to the rotational axis, and torsional loads. The transmission of these types of loads to the drive shaft of the motor causes excessive wear of the motor bearings which is likely to shorten the effective life of the motor.
Another type of diaphragm pump is disclosed in Pleuger U.S. Pat. No. 2,853,015. That patent discloses a diaphragm-type pump in which the connecting rod rides at a lower end thereof against an eccentric cam. A disadvantage with this type of pump is that the sliding friction of the cam against the lower end of the rod creates an area of high friction, which not only generates excessive heat during prolonged operation but requires hardened components which increase the overall cost of fabricating the pump.
Accordingly, there is a need for a diaphragm pump which substantially eliminates the transmission of thrust and torsional loads between the connecting rod and the eccentric drive shaft. In addition, such a diaphragm pump should be relatively inexpensive to manufacture and requires a minimum of parts made from hardened, metallic materials which increase the overall expense of the pump.